Lens and Cataracts Flashcards
the lens is a ____ structure located within the ____
transparent, biconvex;
posterior chamber
the lens is suspended in the posterior chamber via ____
zonules (suspensory ligaments)
the lens focuses ____
light rays to a point source on the retina
the lens contributes ____ of total refractive power of the eye
13-17 D
the lens has a ____ refractive index (____)
high; 1.3-1.4
the lens is composed of ____ and is divided into ____
epithelial cells with a basement membrane;
the embryonic nucleus, fetal nucleus, adult nucleus, cortex, and capsule
during gestation, a single layer of _____ forms a hollow sphere, called the _____
epithelial cells; lens vesicle
_____ cells of the lens vesicle elongate to become primary lens fibers; they fill the lens vesicle and form the ____
posterior;
embryonic nucleus
_____ cells of the lens vesicle near the equator divide to produce new epithelial cells; these cells elongate to become secondary lens fibers and form the ____, which surrounds the ____
cell elongation continues until ____; form ____, allowing cells to remain tightly connected during accommodation
as cells reach the sutures, ____; cells consist of ____
anterior;
fetal nucleus;
embryonic nucleus
nasal and temporal cells meet (suture); interlocking ball-and-socket and tongue-and-groove junctions
nuclei and organelles are degraded; only a cell membrane, cytoskeleton, and crystallins (proteins)
the anterior suture appears as ____, while the posterior suture appears as ____
an upright Y;
an inverted Y
after birth, _____ cells continue to divide and elongate;
secondary lens fibers produced after birth form the ____, which surrounds the ____
newly produced secondary lens fibers are located in the ____
new fibers continue to surround older more central fibers; growth results in concentric layers of _____;
_____ cells are removed from the lens; cells in the center of the lens are ____
anterior;
adult nucleus;
fetal nucleus
cortex
secondary lens fibers;
no;
the oldest cells in the body
the basement membrane of the outer epithelial cells is called the _____; it surrounds ____
lens capsule;
the entire lens
the lens capsule is composed of _____; arrangement makes the lens capsule ____
primarily type IV collagen and GAGs;
highly elastic
____ lens capsule thickens throughout life; lens capsule components are secreted by _____; becomes the ____ BM in the body
anterior;
anterior epithelial cells;
thickest
____ lens capsule remains the same thickness throughout life; no _____ to secrete the lens capsule components
posterior;
posterior epithelial cells
the lens absorbs _____
ultraviolet light
_____ in the lens absorb most of UV-A (320-400 nm) radiation to prevent it from _____; absorption of UV radiation leads to production of ____
chromophores (yellow pigment);
reaching the retina;
free radicals –> DNA damage and protein aggregation
the lens refracts _____
visible light (400-700 nm)
refractive power of the lens changes with ____
contraction of the ciliary muscle
What happens with contraction of the ciliary muscle?
zonules relax –> lens thickness increases –> lens equatorial diameter decreases –> anterior lens radius of curvature decreases (anterior surface curvature steepens) –> lens refractive power increases (> 20D) = accommodation
with age, ability for the lens to change its curvature is ____; ciliary body moves progressively ____; lens _____; lens rigidity ____; nucleus becomes ____ than the cortex
impaired (presbyopia); inward toward the lens; thickens; increases; stiffer
the lens transmits ____
visible light (400-700 nm)
for optimal light transmission, the lens must be ____
transparent
the ____ are the only transparent tissues in the body
lens, cornea, vitreous
contributions to lens transparency
- lack of blood vessels and nerves
- orderly arrangement of lens fibers with uniform spacing between lens fibers; cells are hexagonal, allowing for tight, uniform packing of cells
- few cellular organelles in the visual axis
- high concentration of crystallins
- Na+/K+/ATPase in epithelial cell membranes
- presence of antioxidants glutathione and ascorbic acid (Vitamin C); neutralize free readicals
What are crystallins?
water-soluble proteins that comprise over 90% of total cellular protein; types alpha, beta, gamma;
alpha crystallins function as molecular chaperones - stabilize proteins that are partially unfolded and prevent them from aggregating;
beta and gamma crystallins have unknown functions
with age, the lens loses ____
transparency
with age, chromophore concentration ____;
leads to _____ and _____
increases;
yellowing of the lens;
DNA damage and protein aggregation
with age, glutathione concentration ____;
leads to _____
decreases;
DNA damage and protein aggregation
with age, alpha crystallin concentration ____;
by age 45, _____;
leads to ____
decreases;
no alpha crystallins evident in the lens nucleus;
protein aggregation
with age, epithelial cell membrane permeability ____; leading to ____
increases;
solutes and water enter epithelial cell –> swelling of lens fibers; disrupts orderly arrangement and uniform spacing of lens fibers
nuclear sclerosis
hardening and yellowing of the lens nucleus
nuclear sclerosis etiology
age-related
nuclear sclerosis demographics
everyone, typically begins around age 50
nuclear sclerosis laterality
bilateral > unilateral (can be asymmetric)
nuclear sclerosis symptoms
- asymptomatic
- blurred vision, decreased night vision
- poor color discrimination
nuclear sclerosis signs
- yellow lens nucleus, may progress to brown (brunescent)
- refractive shift, typically a myopic shift (“second sight”)
nuclear sclerosis management
- monitor: 6 month to yearly observation, SL exam, grade severity
- correct refractive error
- refer for cataract surgery when BCVA is 20/40 or worse (most states’ legal driving requirement) or when the cataract is impacting ADLs (vision can be better than 20/40)
nuclear sclerosis pearls
- NS can also be white or “milky”: greater effect on vision, larger myopic shift
- slowly progressive
- can progress to a mature or hypermature cataract
- historically, medical insurance would only pay for surgery when the vision was 20/40 or worse
cortical cataract
opacification of the lens cortex
cortical cataract etiology
age-related
cortical cataract demographics
everyone, typically begins around age 50
cortical cataract laterality
bilateral > unilateral (can be asymmetric)
cortical cataract symptoms
- asymptomatic
- blurred vision
- glare/night vision problems
cortical cataract signs
- cortical water clefts and vacuoles in the early stages
- spoke or wedge-like opacities in the cortex- begin in the periphery, coalesce (get thicker and larger) as the opacities encroach the visual axis
- refractive shift, typically a hyperopic shift, lenticular cyl
cortical cataract management
- monitor: 6 month to yearly observation, SL exam, grade severity
- correct refractive error
- refer for cataract surgery when BCVA is 20/40 or worse (most states’ legal driving requirement) or when the cataract is impacting ADLs (vision can be better than 20/40)
cortical cataract pearls
- slowly progressive
- can progress to a mature or hypermature cataract
- often makes BIO more difficult- glare…
mature cataract
complete opacification of the entire lens
mature cataract etiology
progression of a cortico-nuclear cataract
mature cataract laterality
bilateral > unilateral (usually have cataracts in both eyes, but only one is mature)
mature cataract symptoms
significantly blurred vision (20/400, hand motion, etc.)
mature cataract signs
- complete opacification of the entire lens
- leukocoria (white pupil)
- shallow anterior chamber
mature cataract complications
phacomorphic glaucoma
mature cataract management
refer for cataract surgery
mature cataract pearls
- order B scan to evaluate posterior segment pathology
- not common where there is access to cataract surgery
hypermature cataract (Morgagnian)
mature cataract with liquefaction of the cortex and sinking of the nucleus to the bottom of the lens capsule
hypermature cataract etiology
progression of a mature cataract
hypermature cataract laterality
bilateral or unilateral (usually only one will be hypermature)
hypermature cataract symptoms
significantly blurred vision (probably not seeing much at all)
hypermature cataract signs
- complete liquefaction of the entire lens with the nucleus floating freely in the liquefied cortex
- leukocoria
- shallow anterior chamber
hypermature cataract complications
- lens capsule rupture
- phacolytic uveitis
- phacolytic glaucoma
hypermature cataract management
refer for cataract surgery
hypermature cataract pearls
- order B scan to evaluate posterior segment pathology
- not common where there is access to cataract surgery
posterior subcapsular cataract (PSC)
opacification between the posterior cortex and capsule
posterior subcapsular cataract (PSC) etiology/associations
- age-related
- associated with chronic uveitis, prolonged steroid use, RP, AKC, pathological myopia, radiation, systemic disease (ex: DM, neurofibromatosis)
posterior subcapsular cataract (PSC) demographics
typically begins around age 50 if age-related
posterior subcapsular cataract (PSC) laterality
bilateral > unilateral
posterior subcapsular cataract (PSC) symptoms
- asymptomatic
- blurred vision near > distance (smaller pupil size at near –> PSC fills whole visual axis; often pinhole VA will be worse)
- glare
posterior subcapsular cataract (PSC) signs
- granular or plaque-like opacification anterior to the posterior capsule; commonly begins as a round opacity in the visual axis
- posterior cortical opacification
posterior subcapsular cataract (PSC) management
- monitor: SL exam with retroillumination, grade severity
- cataract surgery when ADLs are affected
posterior subcapsular cataract (PSC) pearls
progresses more rapidly than other senile cataracts (months vs years)*
most common cataracts
- NS
- Cortical
- PSC
anterior subcapsular cataract (ASC)
opacification between the anterior capsule and cortex
anterior subcapsular cataract (ASC) etiology/associations
associated with angle closure (cataract is termed glaucomflecken), AKC, meds (ex: phenothiazines, amiodarone), radiation
anterior subcapsular cataract (ASC) laterality
bilateral > unilateral
anterior subcapsular cataract (ASC) symptoms
- asymptomatic
- blurred vision
- glare
anterior subcapsular cataract (ASC) signs
- granular or plaque-like opacification posterior to the anterior capsule
- anterior cortical opacification
anterior subcapsular cataract (ASC) management
- monitor: SL exam with retroillumination, grade severity
- refer for cataract surgery when BCVA is 20/40 or worse or when the cataract is impacting ADLs
sunflower cataract (chalcosis lentis)
opacification in a sunflower pattern between the anterior capsule and cortex
sunflower cataract (chalcosis lentis) etiology/associations
copper deposition (Wilson disease)
sunflower cataract (chalcosis lentis) laterality
bilateral > unilateral (because of association with systemic disease)
sunflower cataract (chalcosis lentis) symptoms
- asymptomatic
- blurred vision
- glare
sunflower cataract (chalcosis lentis) signs
yellow, green, or red sunflower-like opacification beneath the anterior capsule
sunflower cataract (chalcosis lentis) management
- monitor: SL exam with retroillumination, grade severity
- refer to PCP for evaluation of Wilson’s disease- may resolve with improvement in copper levels
- refer for cataract surgery when BCVA is 20/40 or worse or when the cataract is impacting ADLs
snowflake cataract
white opacities in the cortex
snowflake cataract etiology/associations
DM
snowflake cataract laterality
bilateral > unilateral
snowflake cataract symptoms
- asymptomatic
- blurred vision
- glare
snowflake cataract signs
white, snowflake-like opacities in the cortex
snowflake cataract management
- monitor: SL exam with retroillumination, grade severity
- refer to PCP for evaluation of DM- may resolve with improvement in BG
- refer for cataract surgery when BCVA is 20/40 or worse or when the cataract is impacting ADLs
snowflake cataract pearls
progresses rapidly
Christmas tree cataract (polychromatic cataract)
glittering, multi-colored opacities in the cortex
Christmas tree cataract (polychromatic cataract) etiology/associations
- myotonic dystrophy
- rarely, age-related
Christmas tree cataract (polychromatic cataract) laterality
bilateral > unilateral
Christmas tree cataract (polychromatic cataract) symptoms
- asymptomatic
- blurred vision
- glare
Christmas tree cataract (polychromatic cataract) signs
glittering, multi-colored opacities in the cortex; evolve into typical cortical and/or subcapsular opacities often star-like in conformation
Christmas tree cataract (polychromatic cataract) management
- monitor: SL exam with retroillumination, grade severity
- refer to PCP for evaluation of myotonic dystrophy
- refer for cataract surgery when BCVA is 20/40 or worse or when the cataract is impacting ADLs
the lens and diabetes mellitus
- glucose increases in the aqueous as it increases in the bloodstream –> diffuses into the lens and is metabolized into sorbitol
- refractive error can be changed as plasma glucose level changes; hyperglycemia = myopia, hypoglycemia = hyperopia
- NS and other cataracts may develop earlier than “expected” in the patient with diabetes
other diseases associated with cataract
- myotonic dystrophy
- atopic dermatitis
- neurofibromatosis type 2
- chronic anterior uveitis
- acute angle closure
- high myopia
- hereditary fundus dystrophies
traumatic cataract
- the most common cause of unilateral cataract in young patients
- penetrating trauma
- blunt trauma
- electric shock
- radiation (glassblowers, etc.)
- surgery
cataract surgery procedure
- corneal incision
- removal of a portion of the anterior lens capsule
- removal of the lens
- implantation of IOL
posterior capsular opacification (PCO)
- also called “after-cataract” or “secondary cataract”
- opacification between a PCIOL and posterior capsule
posterior capsular opacification (PCO)
proliferation of lens epithelial cells onto the posterior capsule
posterior capsular opacification (PCO) laterality
bilateral or unilateral
posterior capsular opacification (PCO) symptoms
- asymptomatic
- blurred vision
- glare
posterior capsular opacification (PCO) signs
- PCIOL
- Elschnig’s pearls (round, clear “pearls” on the posterior capsule)
- wrinkling of the posterior capsule
posterior capsular opacification (PCO) management
- monitor: SL exam with retroillumination, grade severity
- neodymium: yttrium-aluminum-garnet (Nd: YAG) laser capsulotomy when ADLs are affected
posterior capsular opacification (PCO) pearls
- most common post-op complication of cataract surgery
- up to 50% of patients develop PCO
- can occur days, weeks, months, or years after surgery
pseudoexfoliation syndrome
systemic disease in which grayish-white material is deposited on anterior segment structures and systemically (e.g., skin, heart, lungs)
pseudoexfoliation syndrome etiology
defect in a gene; codes for an enzyme responsible for the formation of elastin fibers
pseudoexfoliation syndrome demographics
- particularly common in Scandinavians
- incidence increases after age 60 years
pseudoexfoliation syndrome laterality
bilateral or unilateral
pseudoexfoliation syndrome symptoms
asymptomatic
pseudoexfoliation syndrome signs
grayish-white flaky deposition:
- anterior lens capsule- central zone of deposition (often with rolled-up edges), middle clear zone, peripheral cloudy zone
- pupillary margin
- K endothelium
- TM
- anterior hyaloid
- ciliary body
- zonules
- iris sphincter atrophy with TIDs at the pupillary margin
- pigmentation of the TM, at or anterior to Schwalbe’s line (Sampaolesi line), and K endothelium
pseudoexfoliation syndrome complications
- secondary open angle glaucoma: fibrillar material and pigment may obstruct the TM
- secondary narrow angle or angle closure glaucoma: unstable zonules can lead to anterior lens dislocation and narrow angles
- lens (natural or implant) dislocation: zonules are unstable
pseudoexfoliation syndrome management
- monitor q6-12 months for PXF glaucoma: SL exam with retroillumination (retroillumination aids in viewing iris TIDs and lens opacities), grade severity of fibrillar deposition/pigment on anterior segment structures, ASeg photos, IOP, gonioscopy, ON photos, ON OCT, GCC, VF
- if glaucoma develops, treatment is similar to POAG
pseudoexfoliation syndrome pearls
- pseudoexfoliation syndrome is the most common cause of secondary open angle glaucoma
- up to 60% develop OHTN or glaucoma
- affects 2% of US population over age 50 years
